Tube for storage of images



July 29, 1958 E. E. SHELDON TUBE FOR STORAGE 0F IMAGES Filed April 5, 1952 DEFLECTION YOKE FOCUSING CO7 oar-'1.

ECT

CUS

F'ocuslNs Co\ L DEFLECT'lON YOKE DEFLECT'ION YOKE F'OCUSING CON- Fbcusme INVENTOR. 472M622? ZM/VJA'Z 61227001? COIL DEF-'LECTION YOKE- dS atent p T This invention' ;.relates.to the storage of images formed b electromagnetic radiations; and represents acontmuaimpart-f my-co-pending patent application Serial "No 26334631 filed ranua'r 8;1952.

.The primar y object of the present invention. is.:to pro.

" vide a method and device for the storage oi radan or. other invisible images and inspecting themfonadesired I length-of time, when-:wanted." 4

' 'FAn'othen object of: this 'nvention isrto provide amethod and device to produce intensified radar or other electro magnetic 'irnagesi- This intensification will enable-=the overcoming-"of the'ineificiency of: the presentexaminag tions -of riadar images of a lohgpersistene. At'the present leveliof illumination :of the fluorescent radar image of a long persistence, the;human-eye has to rely exclusively onfiscotopic (dark adaptation) vision, which is characterby a; tremendous loss of normal visual acuity in reference both-to detailto thecontrast and to; thespeed of visions The purpose of this invention is to enable the observer'to: use hisphotopic vision, in order to inspect radar or' other images in daylight. 1

- *Another object of this invention is to make it possible to; obtain enlargedradar images 'for examination by many persons. simultaneously.

:Another object of this inventio n' is to increase the sensitivity of radar image receivers to radar or other signals. 'Stillianother object is-"to provide more contrasting radar or: other electromagnetic images than was possible until now in'particular, to obtain the reproduction of halftone's. To-obtain the objects of this invention, a special storage tube hadto be designed. The novel storage tube has. an electron" gun for providing a scanning electron beam, which is modulatedby signals carrying theinformation: to.: be-reproduce d. The modulated electron beam scansa dielectric perforated storage target and produces secondary electron emission therefrom, which may be higher or lower than unity, depending on potentials applied; The secondary electrons are drawn away. As a result, a. positive or negative charge image is stored on dielectric storage surface and may remain thereon for a longtime.

Another electron gun serves to produce a source ofa 2,845,561 if atented July '29, 1958 v broad electrorr'beamand of. the stored charges. can be matched closely and because the broad electron beam does not: discharge stored. charges it will: be .possiblealso to: reproduce half-tones, which will improve the cone trast ofi reproduced pictures, and which wasyanothenobj jectiofzmyinvention; 7 i I Due; to the'factnt-hat fluorescent screenis excitedihyza broad electron beam covering substantiallytheiwhole image'area, insteadiof a scanning electron .beamicovering only one image point, as in other. radar "receivers or kinescopes, a markedly intensified image can'be obtained,

which was. another: purpose: of this invention.

The inventionwillbe better understood wheni taken'iin connection with'the accompanying'drawings.v

Inthe drawingst' A '1 i a Figure 1 represents a diagrammatic crOss-seetiorial viW of the noveli image: tube" r. v Figure 2 represents a modification of the storage target. Figure 3 represents another form of the storage target. Figure 4 represents a cross-sectional view of amodh fication of the storage tube. Figure 5 represents a plan view of the storage'target. Reference will now be made to Fig. l, which. illustrates the new tube 10 t0.v accomplish, the purposes outlined above.' f

The radar 'or ther; signals activate" and modulate cathode 'ray beam 2' from the electron gun 1;] The cathode. 1;.of;'the electron g n. 1 is provided; with a negae tivepotential; The secon no 39 maybe. inqthie tcntialr in relation to hc po ential of the ca hode ofthe V broadielectronbeam. The latterelectron beam is projectecl' on the perforated storage target. The passage of said" broad electron beam through the perforated target iswcontrolled by charges stored in said target. Therefore,

transmitted; electron beam. will have the pattern of the sI IQd charge; image, which has the pattern of the invisible, original image. The broad beamof electrons is focused on the fluorescent screen and reproduces a visible image thereon. Because of dielectric properties of the storage; target, the charge image will persist thereon for a. very'long time, dependent on the type of storage material used. During all this time, the invisible image can bereproducedin a visible form as. a fluorescent image, as; Wasexplained above. In this way, the primary object of the present invention, a storage of images, was

' acconiplished. Because the energies of electrons of. the

fromflof a conducting coating on the inside surface? of;

the tube envelope, and is supplied with a positive poelectron: gun. The P op r op a potentials m y be. applied to the; electrode of the electron gun frompoten; tial so rce 41.. Betwe n. i s. te min ls. 42. n 3,. a n tcn oIncter'or-" bl eder resist nc may e c nne d. in. Olderthat the relative potentials of the various electrodes may beprop y sel t d. The ho z n l and. v rtical scanningirn ti nof h lc tr n in 2. ross cstoreg arg 33; s p ovidcdby h c ion Yoke .2. haying. horizontal and. vertical deflect n. c ls-i The cficct on coils are; energized; by a. cyclically varying; current suitahlewaye. form, wh h may e obtaine from' 'ho zontaladeflection genera or. and froniza v r cal de cc on; enera or D fle tion: ge ors arc w ll kncwnin the; a an re. ther fore not hown. in th d a ings, The a hode; rayi am. ransf rms he r daror other gnals; int a tore charg im ge in; the t g arge 33; The. storag a ge 33,. shown. also n F gnsist.

a ili perf rated. sh et: of me alv or, o h r on uctin material; or of; a wov n nducting; rem sh 3 1a- 0n the'side. ofit-he: arget facing the ele tron gun 5,;therc; is.v depositedby vaporation; a thin coating. p nttlea ageiof; char s. 0n t e pposite, side; is dep sited die electric layer 33b, such as of precipitated silica, silicon dio ide and: titanium dioxide. so; that p rforations. 35: rema n obstructed. The: scanning: c1 ct on.:ieam2. s; n duced: in. the; storage tube 10 by-the lectron. gun: It

an emcdn atcd by: incom ng videdsi na s: car y g h n. ....h et' nio. ma ion.. Th sc nningielec ron. beam 2; sho ld have he finest spot; mpatible with; the required;

ntensity o beam; In some cas s, b tween-th electron storagesurface at: zero-i potential or at cathode potentiali and then to write on it positive, which means to deposit positive charges. This can be accomplished by adjusting the potential of the surface of the storage target, so that its secondary emission is greater than unity. The secondary electrons Will be collected by the collecting anode or by an additional conducting mesh screen disposed in proximity of the storage target and positive charges will be left on the storage surface. These positive charges deposited on the storing surface of the target may be stored thereon for many hours depending on the type of the storage material 33b which was used. Whereas BaF has a time constant of 0.1 second, CaF has the time constant of 50 hours. Also, precipitated silica, silicon dioxide and titanium dioxide may be used for this purpose. The storage target must prevent fading of the stored image, which would cause its disappearance. It must also be free from lateral leakage of stored charges, which would impair resolution of the image.

These conditions are satisfied by equation:

in which R is equal to resistivity of the target in ohm-cm. A=picture area in square centimeters. C==capacitance of the storage target.

T =storage time for one image in seconds. B=thickness of storage target in centimeters.

In case the storage time of three seconds is desired, the electrical resistivity of x10 ohm-cm. will be suitable, if the thickness of target is 1O cm. and picture element is lO square centimeter.

When the stored image is to be read, the electron gun I is inactivated and instead, electron gun 5 is activated. The electron gun 5 produces a broad electron beam 6. The electron beam 6 is slowed down in front of the storage 33 by decelerating electrode 18, which may be in the form of ring electrode or a fine mesh screen. The passage of the broad electron beam 6 through the perforations 35 in the target 33 is modulated by the pattern of deposited charges of said storage target. The greater the positive charge, the more electrons will pass through the openings 35 in the target. The less positive the stored charge, the fewer electrons will be transmitted through these openings. In this way, the electron beam 6 irradiating the storage target will be modulated by the stored image. The transmitted electron beam 6a, therefore, will carry an image. This electron image is accelerated. The accelerating electrode 8 serves to accelerate transmitted electrons 6a to the fluorescent screen 9. The accelerating electrode may be in the form of a ring electrode or in the form of a conducting coating on the inside surface of the glass envelope. The accelerating electrode is provided with a positive potential from an external source of power, as described above.

Next, the electron image may be demagnified if its additional intensification is desired. The electron diminution of the image, in order to gain its intensification, is well konwn in the art and therefore does not have to be described in detail. The diminished electron image is projected on the fluorescent screen 9 at the end of the tube 10, where it can be viewed by the observer directly or by means of an optical magnifying eye-piece 25 or may be photographed. The use of an optical eye-piece to magnify optically the electronically diminished image appearing on the fluorescent screen, is also well known in the art and therefore does not need further description. The fluorescent screen 9 is provided with an electron-transparent conducting backing, such as of aluminum 9a, which improves its efiiciency. On the other hand, if magnification of the radar or other radiation image is needed, it can also be accomplished by electron-optical means. The available energy of the electron image will allow 20-30 times magnification of the image with suflicient luminosity of the fluorescent image. After the stored image has been read and no further storage is desired, it may be erased by the use of the scanning electron beam 2 by adjusting the potential of the storage target to the value at which the secondary electron emission of its storing surface is below unity. In such case, the target will charge negatively to the potential of the electron gun cathode, and will neutralize the stored positive charges. The same results may also be obtained by changing velocity of the scanning electron beam 2.

It is obvious that the image stored in the target 33 may be converted into video signals instead of a fluorescent image. In such case, the electron beam 6 must be focused and must be of a scanning type. Deflection yoke 3 serves to provide the scanning motion of the electron beam 6. Focusing coil 4 serves to produce a fine spot electron beam. The returning nontransmitted electrons 6b are diercted to multiplier 7 for intensification and then are converted into video signals 9 in the usual manner.

A modification of the storage target is shown in Fig. 2. In this embodiment of my invention, the storage target 11 is made of a perforated screen of dielectric material, such as glass, silicon, dioxide or titanium dioxide. The dielectirc material should have, preferably, electrical resistance to satisfy the equation discussed above. The holes 13 in said screen can be produced by photo-engraving methods. The preferred method is to use ionic or electronic etching. The openings must be uniform in size and spacing and should be, preferably, not larger than microns, in diameter. The dielectric storage target may be attached to the walls of the tube by means of metallic rings, or it may be deposited on the mesh screen, as shown in Fig. 1. The supporting mesh screen in some cases may be made of insulating material instead of a conductive material. In some cases, a metallic fine mesh screen 12 connected to the source of potential can be placed in very close proximity to the storage target and then serves to collect secondary electrons emitted from the storage target under impingement of the scanning electron beam 2. Obviously, screen 12 must be disconnected from source of potential in the reading phase of operation when electron gun 5 is activated.

In another modification of my invention, the storage target 11 has a metallic backing 14 deposited on it in such a manner that the openings 13 remain unobstructed, see Fig. 3.

A simplified modification of my invention is shown in Fig. 4. The storage tube 15 has only one electron gun 16. The radar or other signals modulate the electron beam 17. The perforated storage target may be the same as described above and illustrated in Figs. 1, 2 and 3. The electron beam 17 modulated by incoming signals scans the storage target 33 in the usual television raster. The scanning motion of the electron beam is provided by deflecting yoke 19, which has coils in two, perpendicular to each other, planes and which are energized by a sawtooth signal producing generator. The impingement of the electron beam 17 of the target 33 produces secondary electron emission therefrom. The secondary electrons are drawn away either by an adjacent mesh screen or by a conductive coating on the Wall of the tube. As a result, a positive charge image remains on the storing The screen it is activated only in the reading phase of the operation. The passage of said broad electronbeam throughthe perforated target is controlled by charges stored in said target. Therefore, transmitted electron beam a will have the pattern of the stored charge image, which has the pattern of the invisible original image. The broad beam of electrons is acceleratedand'is focused on'the on. Because of dielectric properties of the storage target, the charge image will persist thereon for a very long time, dependent on the type of storage material used. During .all this time, the invisible image can be repro- 'duced in a visible form, as a fluorescent image, as was explained above.

Although particular embodiments and forms of this. invention have been illustrated, it is understood that modi-f .fications may be made by thoseskilled in the art without d'ep'arting from the true scope disclosure. f

I claim: v 1 1. A storage tube comprising in combination a source ,o f electrons,a perforated light-stable storage target for receiving and storing electrons emitted from said source,

"said targetconsisting only of a self-supporting perforated dielectric screen, i means for irradiating said dielectric screen with a beam of electrons and a'luminescent screen .for receiving electrons of said beam transmitted through said perforated screen. I V 2'; A storage tube comprising a perforated dielectric supporting screen, means for irradiating said dielectric screen with a beam of electrons and electron reactive means for receiving electrons of J said beam transmitted throughsaid perforated screen.

3. A storage tube comprising in combination a source layer on a perforated dielectric supporting screen.

5. A storage tube comprising in combination a source -of electrons, a perforated storage target for receiving and storing electrons emitted from said source, said target I consisting only of a perforated dielectric screen, means for irradiating said dielectric screen with a beam of electrons, the source of said beam of electrons being disposed in said tube on the side of said perforated storage target opposite to the side on which said emitted electrons are and spirit of the foregoing fluorescent screen 19 and reproduces a visible image there- 1 image in said target, means for producing a second elec-' tron beam,'said means being disposed in said tubeon the side of said perforated storage target opposite to thersider in combination a source of'electrons, a perforated storagetarget for receiving and storing electronsemitted from said source, said target i consisting of a perforated light-stable dielectric layer on side of said perforated storage target opposite tothe side 1 of the "said electrongun, means for decelerating said I receiving said transmitted electrons.

stored, means for decelerating electrons from said source, and an electron reactive luminescent screenfor receiving electrons of said beam transmitted through said perforated screen.

6. A storage tube comprising in combination an electron gun for producing an electron beam, a perforated storage target consisting only of a perforated self-supporting screen of dielectric material, means for scanning with said electron beam said storage target for producing a stored image in said target, means for producing a second electron beam, means for projecting said second electron beam 'on said target to modulate passage of said beam through said perforated target with's'aid stored image, and an image reproducing luminescent screen for receiving said transmitted electrons.

7. A device as defined in claim 6, wherein said storage target consists. of a perforated dielectric layer anda perforated dielectric supporting screen.

8. A storage tube comprising in combination an elec-' i tron gun for produ'cing an electron beam, a perforated target consisting" only of a perforated self-supporting screen of dielectric material, means-for scanning with said electron beam said storage target for producing a stored of the said electron gun, means for projecting said second electron beam on said target to modulate passage of said beam through saidperforated target with said stored im- ,7

age, and an electronreactive image producing screen for 9. A storage tube comprising in combination an electron gun for producing an electron beam, a perforated target consisting of a perforated self-supporting screen, of dielectricmaterial, means for scanning with said eled,-, tron beam said storage target for producing a stored imagein said target, means for producing a second electron beam, said means being disposed in said tube on the second electron beam, means for projecting said' sec ond electronbeam on said target to modulate passage of said in claim 3, wherein said perforated storage target'consists of 'a perforated dielectric beam through said perforated target .-withsaid stored imageand electron reactive means for receiving said transmitted electrons.

References Citedjinithe file of this patent UNITED STATES: PATENTS A 2,259,507 Iams .Oct. 21,. 2,264,540 Lubszynski Dec.;2, 1941 7 2,280,191 Hergenrother Apr. 21, .1942 2,449,339 Sziklai Sept. 14, 1948 2,458,205 Rose Jan. 4, 1949 2,532,339 Schlesinger Dec. 5, 1950 2,667,596 Szegho et al. Jan. 26, 1954 2,717,971 1955 Sheldon Sept. 13, 

